1. Field of the Invention
The present disclosure relates to a water-air combined passive feed water cooling apparatus and system, and more particularly, to a water-air combined passive feed water cooling apparatus and system for effective cooling, condensing steam of cooling water generated by water cooling through air cooling and refilling the same as cooling water for a heat exchanger of a passive feed water cooling system.
2. Description of the Related Art
After an accident of a light water reactor including a security system configured as an active pump driven using electricity, when a feed water system does not operate, residual heat of a nuclear reactor is removed by driving an auxiliary feed water pump through a steam generator. On the other hand, there is a passive auxiliary feed water cooling system does not need electricity and removes residual heat of a nuclear reactor through a steam generator as a passive apparatus for natural circulation force.
Referring to FIG. 1, since a design of a general passive auxiliary feed water system has a structure, in which when cooling water in a heat exchange cooling tank (PCCT: Passive Containment Cooling Tank) 1 located outside a reactor containment building boils, generated steam 2 is discharged into the air, the cooling ability of the general passive auxiliary feed water system is lost after all the cooling water of the heat exchange cooling tank (PCCT) 1 is evaporated. A cooling time of the passive auxiliary feed water system is designed generally to have 8 hour cooling ability as a reference. However, after Fukushima nuclear accidents, it is necessary for a nuclear reactor cooling system to have about 72 hour cooling ability.
To greatly extend the cooling time of a general passive feed water system from 8 hours to 72 hours or more, it is necessary to design a volume of a cooling tank of the passive feed water system to be greater several times. Accordingly, it is necessary not only to increase a volume of a water tank but also to strongly design supporting structures for the water tank to be resistant to earthquakes.
Also, an auxiliary feed water system using a pump has a possibility of a failure caused by an error of an operator, power failure, the malfunction of the pump.
To overcome such limitations, there is provided a passive auxiliary feed water cooling system capable of increasing security and economic feasibility by passively cooling down residual heat of a nuclear reactor through condensing steam generated from a secondary side of a steam generator when a nuclear reactor accident occurs. For example, there are Korean Patent Registration No. 10-0261752 and Korean Patent Publication No. 2001-0076565, including a vertical isolation condenser of a boiling water reactor, an isolation condenser tank including cooling water and heat-exchangeable with the isolation condenser, a pipe connecting a steam generator to the isolation condenser, and a makeup water tank.
However, general passive auxiliary feed water cooling systems for a light-water nuclear reactor have limitations such as refilling a cooling water tank of a passive auxiliary feed water system with cooling water after all cooling water of the heat exchange cooling tank (PCCT) 1 is evaporated or designing a cooling water tank to be greater several times.
Due to the limitations, it is necessary to provide a water-air combined feed water cooling system extending a cooling water exhaustion time by refilling a cooling tank of a passive feed water system with steam evaporated from the cooling tank and discharged into the air.